A study published in the Science journal found that blood vessels at
the base of owls' heads are able to balloon outwards when blood flow
increases.

This enables them to create "reservoirs" of blood which
are needed to supply the animals' out-of-proportion heads and eyes while
their heads are turned, researchers explained.

In contrast, humans' arteries tend to decrease in size and do not
swell to accommodate greater blood flow, creating the risk of clotting
after sudden neck movements such as whiplash or botched chiropractic
therapy.

Owls were also found to have especially large cavities in their neck
vertebrae through which arteries pass, leaving extra space for movement
when the neck is twisted, and to have small connections between the
carotid and vertebral arteries which allowed blood to pass from one
to the other in the case of one becoming blocked during extreme neck
rotation.